This invention relates to a filter temporarily positionable in a lumen, for example, the lumen of an artery, for trapping and removing particles from a fluid flowing through the lumen while allowing the fluid to flow relatively unimpeded through it.
Various vascular procedures, such as the removal of a stenosis occluding an artery or the positioning of a stent graft to reinforce the weakened artery wall at an aneurysm, tend to dislodge particles or emboli from the wall of the artery. The dislodged emboli become entrained in the blood stream flowing through the lumen of the artery. If allowed to remain in the blood flow, the emboli are carried through the vascular system until they lodge in a blood vessel thereby forming a blockage or embolism. Depending upon the size and/or volume of the emboli and where in the vascular system they lodge, the consequences of an embolism can be extremely serious, resulting, for example, in the sudden cessation of blood flow to an extremity, an organ, such as a kidney, the brain or the heart.
There is clearly a need for a filter which can be temporarily positioned in the lumen of an artery downstream from the point where a medical procedure is taking place which may dislodge emboli from the artery wall. The filter should trap emboli above a predetermined size but allow the blood to flow through relatively unimpeded. The filter should be removable from the artery after the procedure is complete and no further emboli are dislodged, the filter bringing all of the trapped emboli with it out of the vascular system.
The invention concerns an intraluminal filter positionable within a lumen for separating particles from a fluid flowing within the lumen. Although other applications are envisioned, the filter is particularly well suited for vascular use.
In its preferred embodiment, the intraluminal filter according to the invention comprises a first plurality of filamentary members interlaced in a relatively open mesh to form a basket and a second plurality of filamentary members interlaced with one another and with the first filamentary members to form a concave first portion of the basket which is distally positioned and acts as a filter as described below. A second portion of the basket, arranged to face the concave first portion, remains substantially unobstructed and forms openings according to the density of the filamentary members as determined by their size and number, the openings being sized to allow both the fluid and the particles to flow into the concave first portion when the second portion of the basket is oriented upstream within the lumen.
The surface formed by the second filamentary members comprises a filter element having openings of predetermined size smaller than the first named openings in the first portion. The second openings are sized to capture the particles entrained within the fluid while allowing the fluid to flow through the surface.
Preferably, the first filamentary members are formed of a flexible resilient material, such as monofilament wires of the shape memory alloy nitinol. Due to their flexible resilience, the first filamentary members allow the basket to deform elastically from a first shape state to a second shape state. The first shape state has a first diameter sized to allow the basket to slidingly fit within the bore of a catheter positionable within the lumen. The catheter provides the preferred means for positioning the intraluminal filter within the lumen, especially a vascular lumen.
The second shape state has a second diameter substantially larger than the first diameter. The second diameter is sized to allow the basket to sealingly interfit within the lumen and present the filter element substantially across the direction of fluid flow. The basket is biased by internal elastic forces within the first filamentary members to assume the second shape state when released from the catheter.
Preferably, the first filamentary members are interlaced by braiding, a method of interlacing which allows the basket to readily assume the first and second shape states. It is convenient to form the basket by braiding the first filamentary members into a tube having a predetermined length. The tube has oppositely arranged ends which are gathered and cinched to form the basket. Preferably, one of the ends forms the second portion of the basket which is not obstructed by the second filamentary members, thus, forming the first openings at that end.
The second filamentary members are preferably multifilament polyester yarns which allows them to be readily heat sealed to the first filamentary members adjacent to the second portion of the basket. The yarns are also interlaced by braiding with one another and further interlaced with the first filamentary members to secure the filter element formed by the yarns to the basket. The yarns are braided in a relatively closed mesh to form the filter means. The characteristics of the braiding are used to control the porosity of the filter means by tailoring the size of the openings in the filter to capture particles above a predetermined size but allow particles below that size to pass. Thus, emboli in a vascular lumen caused by a surgical procedure can be captured by the filter while components of blood, such as the corpuscles and plasma, will not be significantly impeded.
In an alternate embodiment, the filter includes a plurality of projecting members having end portions projecting angularly outwardly. The end portions are interengagable with the lumen and prevent downstream movement of the filter. The end portions are arranged to point in the downstream direction to allow them to readily disengage from the lumen when the filter is moved in an upstream direction for retraction of the filter into the catheter.
The end portions can be conveniently formed by cutting the selected filaments forming the basket at points adjacent to the concave first portion of the basket. The end portions adjacent to the first portion of the basket are relatively unrestrained by the relatively open mesh of the first filamentary members which allow the ends to project angularly outwardly. The complementary end portions at the second portion of the basket which result from the cut filaments are restrained by the second filamentary members forming the filter element and, thus, do not tend to extend outwardly from the filter. Preferably, the cut filaments forming the projecting members are present in a one to one ratio with the uncut filaments forming the basket.
It is advantageous to attach a flexible tether to the unobstructed end of the basket. The tether has a predetermined length and is extendable through the catheter for allowing the intraluminal filter to be manually withdrawn from the lumen into a catheter bore, for example, after completion of a surgical procedure when the filter is no longer required. The filter, along with the captured emboli, are then removed from the lumen when the catheter is removed.
A preferred method of forming an intraluminal filter according to the invention comprises the steps of:
(a) braiding a plurality of flexible, resilient filamentary members into a relatively open mesh forming an elastically deformable tube, the filamentary members providing a radial bias to the tube, urging the tube to assume a predetermined length and diameter;
(b) interbraiding a multiplicity of yarns with the first filamentary members to form, with the filamentary members, a surface having a predetermined porosity, the surface comprising the filter element or means;
(c) gathering each end of the tube and cinching each end together to form an elastically deformable basket;
(d) removing the yarns from a portion of the basket at one end of the tube, thereby forming openings at the one end which allow the fluid and particles to flow into the filter; and
(e) attaching the yarns to the first filamentary members adjacent to the unobstructed portion of the basket.
Although the steps of removing and attaching the yarns can be accomplished in any of several ways, it is preferred to use a laser to ablate the multifilament yarns from the portion of the basket which is to be unobstructed and use the same laser to heat seal the yarns to the filamentary members adjacent to the unobstructed portion of the basket. The laser allows for pinpoint accuracy in targeting the yarns to be removed and heat sealed.
It is an object of the invention to provide a filter positionable within the lumen of an artery.
It is another object of the invention to provide a filter having a filter element of braided filamentary members to capture emboli above a certain size entrained with the blood in the artery.
It is yet another object of the invention to provide a filter which is elastically collapsible into a first shape state having a diameter sized to permit the filter to slidingly interfit within a catheter bore for positioning the filter within the artery lumen.
It is still another object of the invention to provide a filter which is self-expanding into a second shape state having a second diameter substantially larger than the diameter of the first shape state, the second diameter being sized to allow the filter to sealingly interfit within the artery lumen.
It is again another object of the invention to provide a filter which is collapsible from the second shape state to the first shape state by withdrawing the filter into the catheter bore for removing the filter from the artery lumen.
These and other objects will become apparent from a consideration of the following drawings and detailed description of the invention.